ARTIFICIAL STONE COMPOSITION AND METHOD OF MANUFACTURING ARTIFICIAL STONES

Abstract: The invention provides an artificial stone of the following composition, having a deep color tone and gloss, and a highly dense and uniform structure. An inorganic fine particle component having a size of 10 to 70 mesh is used wherein the sum of the inorganic fine particle component and an inorganic microparticle component having a size of 100 mesh or smaller accounts for at least 85 wt.% of the entire product, and a resin component accounts for up to 15 wt.%. All or part of the fine particle component is surface-coated and hardened in advance by an inorganic or organic substance. The artificial stone of the invention has a uniform composition of the individual components, and fine particles are exposed on the surface by polishing.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to an artificial stone composition and a method of manufacturing an artificial stone. More particularly, the present invention relates to a method of manufacturing a lightweight artificial stone, high in hardness, strength and density which has a surface condition like granite or marble and has properties such as surface hardness and surface wear resistance, and provides an artificial stone useful as a material for a wall, a floor or other building materials, civil engineering materials or a stone column. DESCRIPTION OF THE PRIOR ART A conventional method of manufacturing an artificial stone is to crush stone into appropriate pieces, mix in calcium carbonate and a resin, and then to harden the same. More specifically, Japanese Provisional Patent Publication No. S61-101,443 discloses a method of obtaining a lumpy artificial stone capable of withstanding cutting, which comprises the steps of mixing powdered stone and resins in a vacuum, injecting the mixture into a mold, taking out the molded mixture and subjecting the same to cutting. Another Japanese Patent Publication No. S53-24,447 discloses the manufacture of an artificial stone using powder particles of a natural stone and a synthetic resin. These raw materials are mixed in a prescribed mixing ratio and after placing the raw materials in a mold, are subjected to at least a certain pressure. However, artificial stones obtained by these conventional methods pose a problem in that, in spite of the use of powder particles of natural stone, the color tone or the feeling of depth is not always satisfactory. Conventional artificial stones are defective in that the color tone of the surface inevitably becomes dark and dull. It is conventionally very difficult to achieve a granite-like or marble-like surface provided with a feeling of transparency, depth and size. A conceivable reason is that surface light reflection and absorption differ greatly between artificial stones, depending upon the chemical composition, the particle size and blending ratio of natural stone powder particles. Almost no investigation has been made into such a hypothesis. Further, the chemical composition of an artificial stone largely affects moldability. Depending upon the size or blending ratio of natural stone powder particles blended in an artificial stone or the ratio of binder resin, a problem may be encountered in that fluidity for molding is lost or bubbles remain in the molded body, thus seriously impairing quality and strength of the product artificial stone. To overcome these problems, Japanese Patent Publication No. S53-24,447 proposes fluidization by increasing the amount of resins, which prevents the production of bubbles. However, while increasing the resin content is useful for ensuring a satisfactory fluidity and preventing production of bubbles, this exerts an adverse effect on the properties of the resulting artificial stone. More specifically, the use of a large quantity of resins leads to resinification of an artificial stone product. The resultant product is therefore formed from the natural stone powder particles in resins, and the physical properties thereof are closer to those of the raw material resins than to those of the raw material stone. In spite being called an artificial stone, it is only a resin product having the appearance of a stone. Under these circumstances, there has been a demand for the development of a novel artificial stone which solves the defects of the conventional artificial stones, and when using powder particles of natural stones and the like as raw materials, has a dense structure, gives a feeling of depth, together with a transparent color tone, has the features of a natural stone such as granite or marble, and is easily moldable, permitting the achievement of any shape such as a plate or a rod. SUMMARY OF THE INVENTION The present invention was developed in view of the circumstances as described above, and provides an artificial stone composition comprising a mixed inorganic component which comprises an inorganic fine particle component and an inorganic microparticle component, in which the sum of the inorganic fine particle component, having a size of from 10 to 70 mesh, and the inorganic microparticle component having a size of 100 mesh or smaller accounts for at least 85 wt.% of the entire product, and resin components accounts for up to 15 wt.% of the entire product, wherein all or part of the inorganic fine particle component comprises a transparent fine particle component in which individual particles or particle lumps are previously coated with an inorganic or an organic substance. The present invention also provides an artificial stone molded product, molded by injecting or charging the above-mentioned composition into a mold. The present invention provides furthermore an artificial stone molded product wherein the surface of the molded artificial stone is polished. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in further detail. The raw materials composing the artificial stone of the present invention are broadly divided into the following three components. The main component is an inorganic fine particle component having a size of from 10 to 70 mesh. Appropriate inorganic fine particles are silica, olivine, feldspar, pyroxene, mica and other minerals, natural stones such as granite and metamorphic rock, ceramics, glass and metals. Together with this fine particle component, a microparticle component having a size of 100 mesh or smaller is used. This microparticle component comprises, for example, various natural or artificial microparticle components. Easily available microparticle components include, for example, calcium carbonate and aluminium oxide. As part of this microparticle component, there may be added and blended such components as manganese dioxide, titanium dioxide, zirconium silicate and iron oxide. Antimony trioxide, boron compounds and bromine compounds can be added and blended to impart resistance to flammability. The third component is the resin component. The resin component can be selected from a wide variety of thermoplastic resins. The resin component, can be, for example, acrylate resin, methacrylate resin, and unsaturated polyester resin. The fine particle component of a natural stone is the main factor which affects the appearance and physical properties of the resultant artificial stone. Particularly, partial exposure of an artificial stone, together with the other components, serves as the main factor for exterior color and pattern. Compared with the fine particle component, the microparticle component is much smaller than 100 mesh in size and is present so as to penetrate into spaces between individual fine particles and to fill up these spaces. This component affects properties such as the hardness and flexibility of the resultant artificial stone. The weight ratio of the fine particle to microparticle components is within a range of from 0.5:1 to 5:1. In contrast to the fine particle component and the microparticle component of the natural stone which form the above-mentioned frame, the resin component has a function of contributing to covering these other components, connecting all the components and upon completion of an artificial stone, imparting the necessary elasticity or tensile strength to the product. The ratio of these components is important in the present invention. Particularly important is the ratio of the resin component to the other components. In the present invention, permitting achievement of a highly dense product having a dense structure is one of the features. This high density means that the fine particle component and the microparticle component contained in an artificial stone product are present at a high density, of for example over 2.2 g/cm 3 , which is more dense than conventional artificial stone. More specifically, a higher ratio of fine particles of natural stone forming the frame leads to a product closer to a natural one. A very high ratio makes it difficult for the product to harden and therefore to be used. The resultant product has poor physical properties so that is cannot be used in usual applications. Even use of a higher ratio of microparticle component causes difficulties since the artificial stone may not harden, the product may be poor in gloss, and the resulting product may no longer by rightly called a stone. Therefore, the ratio of the fine particle component and microparticle component to resin component is limited: the ratio must be greater than 85 wt.%, or more preferably, greater than 90%. With a ratio of 95%, the product becomes brittle and barely useful. With a ratio of less than 85%, the product is too soft, thus making it impossible to obtain the properties of a stone, with a scope of application similar to that of a resin plate. This means that the resin component of natural stones should not be present in an amount greater than 15 wt.%. A stone wherein the resin component forms greater than about 15% wt.% makes the product more like a plastic, retaining only the name of artificial stone. An excessively small content of the resin component, although improving the exterior appearance closer to the natural color of the product, makes the product more brittle and not suitable for practical use. Therefore, the amount of resin component should more preferably be within a range of from 3 to 10 wt.%. In the artificial stone composition (and the artificial stone articles) of the present invention, a prerequisite is that all or part of the inorganic fine particle component should take the form of transparent particles, and further, these particles or lumps thereof should previously have been coated with an inorganic or organic substance. The coating layer is partially broken and the coating layer and transparent fine particles are exposed on the product surface. This forms an essential feature of the present invention. Coating of the transparent fine particle component is accomplished by coating and setting of the resin on the surface of the transparent fine particle component, or baking an inorganic substance such as water glass or a glaze for ceramics. In any event, the surface of the transparent fine particle component should have a coating having a thickness of from several µm to several tens of µm, for example, from 5 to 50 µm, or more preferably, from about 20 to 30 µm. More specifically, for example, a coating may be applied using an acrylic resin or an unsaturated polyester resin composition and heating, or irradiating, the resin composition to a temperature of about 150 to 300°C, thereby coating the surface of particles of the fine particle component and hardening the same. Alternatively a coating may be applied using water glass or a glaze, and baking the same to a temperature of about 800 to 1,100°C, thereby achieving an inorganic coating. Such a coating largely improves affinity of the fine particles, serving as aggregates for the artificial stone to the entire structure. The mixture of the microparticle component and the resin component imparts a high strength and leads to a satisfactory surface hardness. More important is the fact that, since transparent natural stones or the like are used for the fine particle component and the surface thereof is covered with a hard coating as described above, polishing the surface of the artificial stone product partially breaks this coating layer. As a result, the surface structure comprises partially exposed inorganic transparent fine particles and the surrounding coating layer gives a unique light reflection effect. That is, the light enters the transparent fine particles, is reflected on the surrounding coating layer and passes again through the transparent fine particles. Such a light penetration and reflection phenomenon is surface in a conventional artificial stone, thus imparting a unique feeling of depths to the artificial stone product of the present invention. Thus, there is available a high-quality marble-like artificial stone having size and depth. The ratio of this transparent fine particle component having the coating layer may be generally within a range of from 10 to 100% relative to the total amount of the inorganic fine particle component blended in the composition of the present invention. In the present invention, the size of the inorganic fine particles should be a prescribed one. More specifically, the inorganic fine particle component should have a size within a range of from 10 to 70 mesh as described above. Except for special cases, a uniform size should preferably be kept. When using colored and colorless particles and the color is darker on the upper or lower side, it is conceivable to use different sizes of fine particles corresponding to colored and colorless ones. Large quantities of excessively different sizes should not be used because of the possibility of deterioration of strength of the product. The microparticles should have, on the other hand, a size of 100 mesh or smaller as described above so as to ensure sufficient penetration between fine particles. It should not therefore be close to that of the fine particles. More specifically, it should preferably be within a range of from 150 to 250 mesh. It is also important that in the high-density artificial stone of the present invention, except for special cases, these materials should uniformly be distributed in any part of the product. It is further required to polish the outer surface of the product. That is, in at least a part of the surface, the coating layer should be partially broken to expose part of the fine particles. Polishing is a convenient way to expose the dense structure and surface depth possessed by the high-density artificial stone of the present invention. Needless to say, a part of the product surface may be polished to expose the fine particle component and the difference from the other part of the same surface may be used as a pattern. When obtaining an artificial stone, the color tone and design of the target natural stone are important. Granite and marble are often used as targets although it is difficult to obtain a product like the natural one with beautiful gloss. In this case, gloss is an important factor determining the value of granite or marble. In natural granite or marble, colors are different and diverse from black to white or to red, and within the same color, the shades are different. When coloring various artificial stones, for example in black, it suffices to use only black powder of natural stones. When using a neutral tint of color, however, there has conventionally been a problem of reproducibility. It has been difficult to reproduce the unique gloss of marble with a satisfactory color. For example, even when using a dye or a pigment for coloring, it has conventionally been difficult to impart gloss or depth. In the present invention, on the other hand, a transparent fine particle component is used. When desiring to achieve the gloss of granite or marble, fine particles obtained by milling a natural quartz stone may be used as the fine particle component. Fine particles obtained by milling a natural quartz stone have a unique flat and smooth portion on the surface because the raw material is quartz. Particles are often.colorless and transparent. The color, if any, is not a strong one, and if not transparent, particles often retain transparency to some extent. By using this raw material, it is possible to control the color of the product by means of the color tone of the coating layer and the resin component, and impart depth and gloss to the color by the presence of a transparent quartz fine particle component. When, for example, the coating layer is a water glass baked layer containing a white pigment, or when the stone has a hardened layer of an unsaturated polyester resin and an unsaturated polyester resin is used as the resin component, the resin has a slightly yellowish white appearance in general, leading to a glossy product, milk white in colour. There is therefore available a product having a color tone close to a milk white natural marble. By using a coating layer containing a coloring agent such as a pigment or a dye and further adding an inorganic pigment such as titanium dioxide, zirconium silicate, manganese dioxide, iron oxide or cobalt oxide, an organic pigment such as an azo-pigment or a phthalocyanine pigment, or any of various dyes to the resin component, there is available a product having a uniform color with a unique tone with depth and gloss. In the artificial stone composition of the present invention, a color particle component which is substantially the same size as the fine particle component may be used in the mixture to impart a color to the product. In any event, it is possible to ensure color reproducibility far more easily than in the conventional artificial stones. The stone is reproduced without discoloration and a product excellent in depth and gloss is available. In the artificial stone of the present invention, it is particularly effective to apply a glaze of coloring ceramics to the powder particles of the natural transparent fine particle component, baking the same into powder particles of a desired color, and using these particles as the fine particle component. By this method, it is possible not only to ensure a desired color, but also to have a wide choice of colour. When milling natural quartz stone to the same size as the fine particle component, applying a glaze thereon and baking the same, there are no problems for colors such as black and red, and the color is obtained with gloss and tone reproduced perfectly, thus providing advantages unavailable in the conventional coloring method. In any event, the fine particle component having a coating layer formed by baking is used in a ratio within a range of from 10 to 100% of the total fine particle component. A short fiber component may be blended to reinforce the structure of the formed product, although the fibre should not affect the color tone of the artificial stone. For example, applicable fibers include glass fiber, ceramic fiber, metal fiber and resin fiber. Glass fiber is particularly favorable for this purpose. Short fibers having a diameter of from 10 to 100 µm, and a length of from 1 to 10 mm are usually used in an amount within a range of from 1 to 10 wt.% relative to the fine particle component. The high-density artificial stone of the present invention having excellent color properties may be of any shape such as plate, rod or cylinder. A forming method can be selected from a wide variety of methods including, for example, mold injection and compression molding. An important point in the manufacturing method of the present invention is that the mold used is not a closed mold. The open portion should be clearly a part relative to the total surface area. For example, for a square cylinder, a mold in which the portion forming the edges of a plate is opened should preferably be used with the opening side above the other sides. An opening side may also be accomplished, in addition to that described above, by making the narrower side semi-open, i.e., for example, by forming this side in a mesh-shaped form so as to prevent easy outflow of the fine particles. When injecting a uniformly mixed fluid of the resin component, fine particle component and microparticle component into a mold formed as described above, it is advantageous to reduce the inner volume of the mold after injection with a view to reducing the resin content in the resultant artificial stone while ensuring a sufficient fluidity upon injection. More specifically, for example, when the mold interior is flat, the flat walls are brought closer together to reduce the thickness. As a result of this reduction of the inner volume, the resin component flowing out the mold gathers in the open portion and further flows out through the open portion or by reducing the inner volume by pushing up the bottom portion after injection, the resin component in the upper portion flows out. Since the resin component has a higher specific gravity than the fine particle component or the microparticle component, it begins to sink down upon injection into the mold, and sinking rapidly proceeds because of a large difference in the specific gravity. By reducing the inner volume, only the light resin component is pushed out and gathers at the open portion. The resin component can therefore be taken out in a controlled amount using a mold of a prescribed inner volume, and then reducing the inner volume by a prescribed amount. The amount of resin component upon solidification of the formed artificial stone is thus smaller than the amount of resin component upon injection, and the amount of resin component in the product can be reduced from that upon injection. Compression molding is also effective as a manufacturing method in the present invention. Compression molding comprises the steps of injecting a material (mixed material) formed by blending and kneading the fine particle component, the microparticle component and the resin component in necessary amounts, adding the mixture to the lower half of a horizontal mold, placing the upper half of the mold onto the lower half, and pressing the mold under a surface pressure within a range of from 4.9 x 10 5 to 9.8 x 10 6 Pa (5 to 100 kgf/cm 2 ). In this molding, the material is heated to a temperature of about 90 to 140°C for a period of about 5 to 20 minutes during compression. In compression molding, while heating the mold it may be vibrated and placed under pressure to improve the fluidity of the mixed material in the mold. Compression molding as described above, is suitable for mass production as a molding method for relatively simple shapes, and is economic as there is almost no loss of material. In the present invention, the surface of the molded product is processed after the completion of molding so as to expose the fine particle component to the surface. A first practice for this purpose is selective removal of the resin component. It is effective, after stripping off the mold, to subject the molded product surface to a high-pressure water jet to apply a surface processing. This processing is not limitating, varying with the thickness, distance from the nozzle, processing form and various other conditions. In a usual case with a thickness within a range of from 2 to 20 cm, water of a pressure within a range of from 50 to 800 kg/cm 2 may be ejected from a nozzle height of about 2 to 10 cm. This water pressure is lower than that for a natural stone. The presence of the resin component permits easy and high-grade processing. There is practically no limit on the nozzle and the system thereof for the ejection of high-pressure water. Any of various ones may be adopted. This surface processing achieves flattening or roughing of the surface by means of the water jet, and an artificial stone with depth and size is thus available. The presence of the resin component eliminates the risk of surface clouding and, as compared with the etching technique using chemicals, it is easier to dispose the waste liquid. Needless to say, the surface may be treated with an organic solvent and the resin component may partially be removed by softening or melting. Depending upon the resin component used, the organic solvent in this case may be selected, from for example, a halogenated hydrocarbon such as ethylene chloride, methylene chloride, and chloroform, a carboxylic acid such as acetic anhydride, ethyl acetate, and butyl acetate, and esterified compounds thereof, acetone, tetrahydrofuran, DMF, and DMSO. Surface irregularities can be formed by immersing the molded product into the organic solvent, or spraying or pouring the organic solvent, and removing softening or melting portions of the resin component from the surface. Surface irregularities may also be formed by scraping the lower-hardness portion of the resin component from the surface by means of a wire brush or cutting. After roughing the surface and applying a surface processing with any of the various means described above, the coating layer of the fine particle component on the surface is partially broken, as described above, and this coating layer and the fine particles are exposed on the product surface as a sectional face. This permits achievement of a unique depth and glossy and massive surface. This is caused by a unique reflection of light as already described above. There is no particular limit on the means for surface polishing: tools such as a grindstone, a grinding cloth or a grinding belt may be use, or grinding agents such as a buff grinding agent or a rubbing compound. As the grinding agent, any of diamond, boron carbide, corundum, alumina and zirconia, of the type normally used for polishing, tripoli , dolomite, alumina, chromium oxide and cerium of the type normally used for grinding and polishing may appropriately be selected for use. After such polishing, the surface may of course be further roughened to form irregularities. In this case also, at least part of the fine particles and the coating layer thereof must be exposed in section. By all these operations, there is manufactured a massive artificial stone, excellent in surface condition. Now, some examples of application of the present invention will be described below. The present invention is not limited by the following examples. EXAMPLES Example 1 Natural silica stone particles having a particle size of from 10 to 25 mesh each provided with a surface baking layer having a thickness of about 30 µm made at about 1,000°C by the use of a white glaze, were used as 50 wt.% of the total fine particle component. The fine particle component and 230 mesh calcium carbonate were uniformly mixed, in a weight ratio of 2:1 so as to account for 90 wt.% of the total weight of the composition, together with 9 wt.% polymethylmethacrylate resin and 1 wt.% setting agent into a mortar-like mixture. This composition was injected into a mold to form a plate-shaped product having a thickness of about 15 mm. Then, the surface was polished by means of a corundum polishing agent. As a result, the fine particle component having baked coating layers was partially exposed as a partial sectional face of the baked layer and the fine particle component. The resultant artificial stone had a deep marble-like milk white color and gloss, free from internal and surface bubbles with a uniform composition. In a test carried out in accordance with the Japanese Industrial Standards JIS K-7112, a specific gravity of 2.29 was shown. The product had a water absorption of 0.13%. The other properties were as shown in Table 1. Item Result Test condition Bending strength 3.7x10 6 Pa (31.30 kgf/cm) Based on JIS A5209 Compression strength 1.37x10 8 Pa (1400 kgf/cm 2 ) Cross-head speed: 0.5mm/min Load cell : 2 tons Impact strength 4.58 kgf - cm/cm 2 Pendulum impact tester Hardness 1.00x10 10 Pa (1021 kgf/mm 2 ) Vickers hardness based on JIS Z-2244 Linear expansion coefficient 0.65 (x10 -6 K) TMA (30 ∼ 100°C) Wear resistance 0.03g Sand dropping wear resistance test based on JIS A-1452 In a immersion test into a 3% aqueous hydrochloric acid solution for eight hours and into a 3% aqueous sodium hydroxide solution for eight hours, no abnormality was observed. When using the resultant product as a wall plate for a building, a beautiful marble-like stone having depth was obtained. Example 2 The same conditions as in the Example 1 were employed except that the sum of the fine particle and microparticle components was 93%, a resin component of 6%, and a thickness of the surface baking layer of 20 µm were adopted. As in the Example 1, a high-quality artificial stone was obtained. It had a compression strength of 1.36 x 10 5 Pa (1.385 kg/cm 2 ), a hardness of 1.01 x 10 10 Pa (1,025 kgf/mm 2 ) and a marble-like depth and excellent surface. Example 3 A 15% portion of the total amount of a fine particle component of natural silica stone was coated with a blue glaze in a thickness of 25 µm on the particle surface. Using this fine particle component with a size within a range of from 10 to 50 mesh, a plate-shaped body was molded in the same manner as in Example 1. The resultant product was polished with an alumina-zirconia polishing agent. A deep and beautiful blue-white surface was obtained. The product had physical properties substantially the same as those in the Example 1, thus achieving a high-quality artificial stone as a building material Example 4 65% of the total amount of a fine particle component of natural silica stone having a size of from 10 to 50 mesh, a polymethylmethacrylate resin mixed with a cobalt blue (Pig Blue 28) pigment were set with a coating having a thickness of about 50 µm. Molding was conducted in the same manner as in the Example 3, and then the surface was polished. A deep and beautiful surface tinted with blue and milk white in mixture was obtained. This artificial stone product had a specific gravity of 2.29, a bending strength of 2.99 x 10 6 Pa (30.55 kgf/cm 2 ) a compression strength of 1.28 x 10 5 Pa (1.305 kgf/cm 2 ) and a hardness of 9.32 x 10 9 Pa (950 kgf/mm 2 ). Comparative Example 1 The same steps as in the Example 1 were followed except that a fine particle component of 5 to 20 mesh was used. The resultant molded product showed an insufficient strength and was observed to have a nonuniform structure. Comparative Example 2 Samples with weight ratios of the fine particle component to the microparticle component of 0.2:1 and 6:1 were prepared under the same conditions as in the Example 1. None of these samples showed a uniform and dense structure, or had practically satisfactory strength properties. Comparative Example 3 The conditions in the Example 3 were followed except that the resin component accounted for 20 wt.%. The sample showed not only reduced hardness properties, but also a tendency to suffer flaws. A feeling of a natural stone was not produced, the stone appearing more like a resin product. Comparative Example 4 The same steps as in the Example 4 were followed without providing a coating layer on the fine particle component, and a product was molded by blending a green pigment into the resin component. Green tone was excessive and the surface feeling of a natural stone was lost. Example 5 A fine particle component containing about 80% natural silica stone particles of 10 to 50 mesh with a surface coating of a thickness of about 30 µm provided by baking water glass containing red pigment (iron oxide), and a microparticle component comprising a mixture of 100 to 350 mesh calcium carbonate and aluminum hydroxide at a ratio of 50:50 were mixed at a weight ratio of 2:1, and an unsaturated polyester resin added with a red pigment was mixed therein to account for 90% of the total weight. This mixture was injected into a mold and compression-molded under a surface pressure of 10 kgf/cm 2 , and the surface was polished with a corundum polishing agent. A red artificial stone product, excellent in color tone and depth was obtained. It had satisfactory strength properties including a bending strength of 3.14 x 10 6 Pa (32.05 kgf/cm 2 ), a compression strength of 1.38 x 10 5 Pa (1.405 kgf/cm 2 ), and a hardness of 1.04 x 10 5 Pa (1.062 kgf/mm 2 ). INDUSTRIAL APPLICABILITY According to the present invention, as described above, there is provided a high-density artificial stone having a deep and glossy color tone and satisfactory properties so far unavailable. The resulting product exhibits a uniform quality which is hard to obtain in a natural stone. In addition, manufacture of such an excellent product is possible without particularly expensive facilities. Particularly, the artificial stone of the present invention is suitable for obtaining granite or marble-like products, and can be applied in the same manner as in a natural stone. The high quality product is applicable as a wall material, floor material and column material more widely than natural stones.

Claims: An artificial stone composition comprising a mixed inorganic component which comprises an inorganic fine particle component and an inorganic microparticle component, wherein the sum of the inorganic fine particle component having a size of from 10 to 70 mesh and the inorganic microparticle component having a size of 100 mesh or smaller accounts for at least 85 wt.% of the entire product and a resin component accounts for up to 15 wt.% of the entire product, wherein the fine particle component and the microparticle component are blended at a weight ratio within a range of from 0.5:1 to 5:1 and wherein all or part of the inorganic fine particle component comprises transparent fine particle component in which individual particles or particle lumps are previously coated with a coating layer of an inorganic or an organic substance the coating layer is partially broken and the coating layer and transparent fine particles are exposed on the product surface. An artificial stone composition as claimed in claim 1, wherein said coating layer has a thickness within a range of from 5 to 50 µm. An artificial stone composition as claimed in either one of claims 1 or 2, wherein at least 10% of the total amount of the fine particle component have surface coating hardened layers. An artificial stone composition as claimed in claim 1, wherein the fine particle component has a surface coating hardened layer formed by baking with water glass or water glass added with a pigment, or a glaze for ceramics. An artificial stone composition as claimed in claim 1 wherein said composition has a surface coating hardened layer comprising a resin added with a pigment. An artificial stone composition as claimed in any one of claims 1 to 5, wherein the ratio of the resin component is in the range of from 3 to 10 wt.%. An artificial stone article comprising the composition as claimed in any one of claims 1 to 6. An artificial stone article comprising the composition as claimed in any one of claims 1 to 6 wherein the surface is polished. A method for manufacturing an artificial stone comprising the composition as claimed in any one of claims 1 to 6, comprising the steps of injecting said composition in a mold to cause hardening, and then polishing the surface thereof to break the coating layer partially exposing the coating layer and the transparent fine particles on the produce surface. A method for manufacturing an artificial stone comprising the composition as claimed in any one of claims 1 to 6, comprising the steps of injecting said composition into a mold, applying a pressure, heating the same to harden, and then polishing the surface thereof. A manufacturing method according to claim 10, wherein the composition is heated and hardened under a pressure in the range of from 4.9 x 10 5 to 9.8 x 10 6 Pa (5 to 100 kgf/cm 2 )at a temperature in the range of from 90 to 140°C. A method for manufacturing an artificial stone as claimed in either one of claims 9 or 10, wherein a surface processing is applied prior to polishing.

Inventors: SAKAI TSUYOSHI, SAKAI, TSUYOSHI, SAKAI, Tsuyoshi-Doppel Co., Ltd.
Applicants: DOPPEL CO LTD, DOPPEL CO. LTD.
Application year: 1994
Main classification: C04B26
IPC codes: C04B26